Polyolefin foams and methods of making the same

ABSTRACT

A non-crosslinked polyolefin foam comprises a plastics component and a blowing agent. The plastics component comprises a first constituent and a second constituent. The first constituent is a Ziegler-Natta catalyzed linear low density polyolefin and the second constituent is a low density polyolefin in one embodiment. The Ziegler-Natta catalyzed linear low density polyolefin has a polydispersity of less than 10 and a melt flow index less than 10 g/10 minutes. The second constituent may be a polypropylene

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of UK Patent Application No.0228476.8 entitled “Improvements Relating to Foam Materials” filed onDec. 6, 2002.

FIELD OF THE INVENTION

[0002] This invention is concerned with improvements relating to foammaterials, including low density polyolefin foam materials, of the kindthat may be utilized as packaging and/or cushioning materials. Moreparticularly, the invention is directed to manufacturing closed-cellplastics foam.

BACKGROUND OF THE INVENTION

[0003] A closed-cell plastics foam is hereinafter defined as one inwhich the majority of the cells are closed. Typically, a closed-cellfoam of a reasonable quality has at least 70% closed cells, and aclosed-cell foam of a good quality has at least 85% closed cells,although this may be less in thin sheets (e.g., 1 mm or less).

[0004] A conventional starting material used in manufacturing lowdensity polyolefin foam is a polyolefin resin such as a highly-branchedlow density polyethylene (LDPE), typically manufactured by ahigh-pressure radical polymerization process, such as, for example,tubular autoclave. In this process, the monomers are mixed thoroughlyunder high pressure and at a high heat that induces polymerization, andforms a polyethylene resin.

[0005] To produce a foam, this polyethylene resin, typically inpelletized form, is then plasticized in a screw extruder, and mixed witha blowing agent. When the material is extruded into, for example, asheet form, the blowing agent expands, which produces a large number ofsmall bubbles.

[0006] Where the polyethylene foam is used as a packaging material,while some physical strength characteristics are important, cost is veryimportant, and over many years, much effort has been put into reducingcost.

[0007] To date, a majority of the effect in reducing the cost has beendirected towards lowering the foam density and, by conventionaltechniques, it is possible to produce a material having a density as lowas 15 to 20 kg/m³.

[0008] Alternative materials have been considered in an attempt tofurther reduce the cost. In particular, a number of attempts have beenmade to use a linear low density polyolefin such as a linear low densitypolyethylene (LLDPE). LLDPE is typically manufactured at a lowerpressure and a lower heat, using catalysts. At this time, LLDPE isapproximately 10% less expensive than LDPEs.

[0009] However, conventional Ziegler-Natta LLDPE, hereinafter defined asLLDPE manufactured without using a metallocene (or a similar substance)as a catalyst, contains predominantly linear polymer chains withirregular short-chain branching and no substantial long-chain branching.Conventional Ziegler-Natta LLDPE has a narrow molecular weightdistribution (MWD), which results in the material having poor foamingcharacteristics, specifically having a lower melt strength.

[0010] LLDPE may be produced by using different catalyst systems, (e.g.,a metallocene catalyst), which can lead to producing polymers havingsubstantial long-chain side branching. This long-chain side branchingresults in a material having a broad MWD and a higher melt strength.This method consequently has a higher cost. Such LLDPE may be blendedwith LDPE to produce a material that may be foamed to the required lowdensity. Metallocene catalyzation, however, is an expensive process, andthe cost of such modified LLDPE results in a material that is in factmore expensive than LDPE itself.

[0011] Alternatively, it is possible to add cross-linking agents such asorganic peroxides to the LLDPE/LDPE mix, which again increase the extentof long-chain branching and the melt strength of the mix. However, theseadditional compounds are also expensive.

[0012] Attempts have been made to produce a foam from a blend of smallquantities of conventional Ziegler-Natta LLDPE with LDPE, but it hasbeen found that the melt strength of the blend is increased and sodifficulty is encountered in achieving as low of density as is obtainedusing 100% LDPE, again resulting in a higher cost outweighing thesavings resulting from using LLDPE.

[0013] Thus, it would be desirable to have a foam that overcomes atleast some of the above-noted shortcomings of existing LDPE foam blends.

SUMMARY OF THE INVENTION

[0014] Surprisingly, it has been found by the present applicant that,when LLDPE is blended in higher amounts with LDPE, a material isproduced that may be foamed to a low density foam product. Such a lowdensity foam product does not increase in density compared with theproduct obtained using 100% LDPE. Additionally, it has been found by thepresent applicant that, when the foaming process is slightly modified,it is possible to produce a material that has good foamingcharacteristics and a low density, even when blending small amounts ofLLDPE with LDPE. In this manner, small but significant savings may beobtained in manufacturing polyethylene foam.

[0015] Additionally, by using LLDPE, an increase in the toughness andelasticity of the foam is obtained, providing a higher degree ofprotection during, for example, transportation of the article.

[0016] According to a first aspect of the invention, there is provided apolyolefin foam comprising a plastics components and a blowing agent.The plastics component consisting primarily only of a first constituentand a second constituent, wherein the first constituent is aZiegler-Natta catalyzed linear low density polyolefin and the secondconstituent is a low density polyolefin. Preferably, the secondconstituent is a low density polyethylene.

[0017] According to a second aspect of the invention, there is provideda polyolefin foam comprising a plastics component and a blowing agent.The plastics component consists primarily only of a first constituentand a second constituent, wherein the first constituent is aZiegler-Natta catalyzed linear low density polyethylene and the secondconstituent is a polypropylene. Preferably, the second constituent is ahigh-melt strength polypropylene. The plastics component consistsprimarily of the mixtures specified above. This means that althoughother substances may be present in trace amounts, such trace substancesare not thought to effect the foamability of the plastics component.

[0018] Additionally, nucleating agents and aging modifiers may beincorporated in a conventional manner.

[0019] The plastics component may consist primarily of from 1% to 85% byweight of the first constituent, and from 99% to 15% by weight of thesecond constituent.

[0020] Alternatively, the plastics component may consist primarily offrom 5% to 10% by weight of the first constituent, and from 95% to 90%by weight of the second constituent. Alternatively, the plasticscomponent may consist primarily of from 10% to 15% by weight of thefirst constituent, and from 90% to 85% by weight of the secondconstituent.

[0021] Alternatively, the plastics component may consist primarily offrom 15% to 20% by weight of the first constituent, and from 85% to 80%by weight of the second constituent. Alternatively, the plasticscomponent may consist primarily of from 20% to 25% by weight of thefirst constituent, and from 80% to 75% by weight of the secondconstituent.

[0022] Alternatively, the plastics component may consist primarily offrom 25% to 30% by weight of the first constituent, and from 75% to 70%by weight of the second constituent. Alternatively, the plasticscomponent may consist primarily of from 30% to 35% by weight of thefirst constituent, and from 70% to 65% by weight of the secondconstituent. Alternatively, the plastics component may consist primarilyof from 35% to 40% by weight of the first constituent, and from 65% to60% by weight of the second constituent.

[0023] The foam may have a density of less than 90 kg/m³, convenientlyless than 50 kg/m³, preferably having a density of less than 30 kg/m³,and most preferably having a density of less than 20 kg/m³.

[0024] Preferably, the second constituent consists primarily of apolyethylene. Alternatively, the second constituent may consistprimarily of a polypropylene, preferably a high-melt strengthpolypropylene.

[0025] According to a third aspect of the invention, there is provided amethod of manufacturing a polyolefin foam. The method involves mixing asresin constituents primarily only a first constituent and a secondconstituent in an extruder, adding a blowing agent to the resultantmixture, and extruding the resultant mix into foam form. The firstconstituent is a Ziegler-Natta catalyzed linear low density polyolefinand the second constituent is a low density polyolefin. Preferably, thesecond constituent is a low density polyethylene.

[0026] According to a fourth aspect of the invention, there is provideda method of manufacturing a polyolefin foam. The method involves mixingas resin constituents primarily only a first constituent and a secondconstituent in an extruder, adding a blowing agent to the resultantmixture, and extruding the resultant mix into foam form. The firstconstituent is a LLDPE and the second constituent is a polypropylene.Preferably, the second constituent is a high-melt strengthpolypropylene.

[0027] The first constituent may be present in an amount from 1% to 85%by weight of the total polyolefin content.

[0028] Alternatively, the first constituent may be present in an amountfrom 5% to 10% by weight of the total polyolefin content. Alternatively,the first constituent may be present in an amount from 10% to 15% byweight of the total polyolefin content.

[0029] Alternatively, the first constituent may be present in an amountfrom 15% to 20% by weight of the total polyolefin content.Alternatively, the first constituent may be present in an amount from20% to 25% by weight of the total polyolefin content.

[0030] Alternatively, the first constituent is present in an amount from25% to 30% by weight of the total polyolefin content. Alternatively, thefirst constituent may be present in an amount from 30% to 35% by weightof the total polyolefin content. Alternatively, the first constituent ispresent in an amount from 35% to 40% by weight of the total polyolefincontent.

[0031] Preferably, the polyolefin foam is a closed-cell polyolefin foam.

[0032] Using the methods discussed above, the foam may be extruded to adensity of less than 90 kg/m³, conveniently less than 50 kg/m³,preferably being extruded to a density of less than 30 kg/m³, and mostpreferably being extruded to a density of less than 20 kg/m³.

[0033] Preferably, the second constituent consists primarily of apolyethylene. Alternatively, the second constituent may consistprimarily of a polypropylene, preferably a high-melt strengthpolypropylene.

[0034] Preferably, in carrying out the method, the first constituent hasa density of from 900 to 950 kg/m³, and preferably from 917 to 930kg/m³.

[0035] Preferably, also the difference in the crystallizationtemperatures of the two resinous constituents of the foam is greaterthan 8° C., preferably greater than 10° C., and preferably greater thanabout 12° C.

[0036] Preferably, the first constituent has a melt flow index(according to ISO 1133) of less than 10 g/10 minutes, conveniently lessthan 5 g/10 minutes, and preferably less than 3 g/10 minutes.Preferably, the first constituent has a polydispersity of less than 10,conveniently less than 8, and typically less than 5.

[0037] The method may involve incorporating nucleating agents and agingagents.

[0038] Preferably, the methods discussed above involve using atwin-screw extruder. In this manner, an extrudable mixture may beobtained with lower levels of shear force than would be involved byusing a single-screw extruder, allowing effective mixing to be obtainedat a lower temperature than would otherwise be the case.

[0039] Preferably, the method involves controlling the melt temperatureof the resin constituents. This may involve ensuring that the melttemperature is compared, preferably matched, to a pre-determined datum,and in this case, the datum is preferably derived from the melttemperature resulting when 100% of the second constituent is used.

[0040] By using the first constituent, an increase in the toughness andelasticity of the foam is obtained, providing a higher degree ofprotection during, for example, transportation of the article.

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Embodiments of this invention will now be described, by way ofexample only, with reference to the accompanying drawings in which:

[0042]FIG. 1 is a graph that shows schematically the variation in forceat break for different percentage blends of LDPE and LLDPE resin, andthree different material blends;

[0043]FIG. 2 is a graph that shows schematically the variation invelocity at break for different percentage blends of LDPE and LLDPEresin, and for three different material blends;

[0044]FIG. 3 is a graph that shows schematically the variation in forcegenerated at different pull-off speeds for different percentage blendsof LLDPE and LDPE resin; and

[0045]FIG. 4 is a graph that shows schematically how force anddrawability vary with different blends of LLDPE and LDPE resin.

[0046] While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof have been shown by wayof example in the drawings and will herein be described in detail. Itshould be understood, however, that it is not intended to limit theinvention to the particular forms disclosed but, on the contrary, theintention is to cover all modifications, equivalents, and alternativesfalling within the spirit and scope of the invention as defined by theappended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS/EXAMPLES

[0047] Initial experiments were conducted on blends of LDPE and LLDPEresin. FIGS. 1 to 3 show examples of the results of these initialexperiments. The LDPE was produced by the high-pressureradical-polymerization process. Alternatively, it is contemplated thatLDPE may be produced by other processes. The LLDPE used was conventionallow-pressure Ziegler-Natta catalyzed LLDPE without using metallocenes orsimilar substances as a catalyst. The particular LLDPE used in theseexamples was produced with a C₄ co-monomer. It is believed that theresults would be equally applicable to LLDPEs produced from otherco-monomers, such as C₆ or C₈ co-monomers.

[0048] The blends consist primarily only of LDPE and LLDPE. This meansthat although other substances may be present in trace amounts, suchtrace substances are not believed to affect the characteristics of theblends shown in the graphs.

[0049] Referring initially to FIG. 1, the force at break of a resin is ameasure of the melt strength of the foam. An increase in melt strengthmeans that it is possible to expand the foam to a higher degree, butalso means that the foam tends to be closed cell rather than open cell.Traditionally, the problem with adding LLDPE to LDPE is that ineffectiveopen-celled foams are produced.

[0050] There is, however, also an upper limit to the melt strength of afoam in that the extra gas that must be used to expand such a foam willcool the polymer mix more quickly. Thus, the foam needs to be expandedmore rapidly without significant resistance.

[0051] The data shown in FIG. 1 was produced by testing resin thatcomprises blends of different percentages of LDPE and LLDPE. Trendlines,as shown, have been formed by extrapolating the data points using asecond order polynomial.

[0052] As shown in FIG. 1, the force at break for a 0% LLDPE resin(i.e., 100% LDPE resin) is significantly greater, being around six timesgreater, than the force at break for a 100% LLDPE resin. This is whyfoams containing large amounts of LLDPE have been previously found to beineffective, and is one of the reasons why one would expect the meltstrength of a blend of LLDPE and LDPE to be lower than the melt strengthof a foam that consists only of LDPE.

[0053] The lower melt strength of conventional LLDPE is thought to bedue to its lack of long chain branches, which provides an insufficientmelt strength to allow successful foam formation. Thus, previousattempts to improve the melt strength of LLDPE foam have focused onusing, for example, metallocene-catalyzed LLDPE, which has greaterhomogeneity and a greater number of long-chain branches, or increasingthe long branching using cross-linking agents, as outlined earlier.

[0054] However, as is also shown in FIG. 1, surprisingly, the force atbreak of a resin that consists of a blend of LLDPE and LDPE can actuallybe greater than the force at break of either 100% LDPE or 100% LLDPE.This implies that such a blend, although more difficult to foam, couldactually produce a less dense foam, since it is possible to retain alarger volume of blowing agent in the foam without the bubbles breaking.Thus, the measures used in previous attempts may not actually benecessary.

[0055] The greater strength, in the film at least, seems to be producedin blends that contain between approximately 1% LLDPE and approximately85% LLDPE. The greatest strength resin seems to be produced at around40% LLDPE, depending on the type of LDPE and LLDPE used.

[0056]FIG. 2 can be seen to follow the same general trend as FIG. 1. Thevelocity at break can be considered to be indicative of the resilienceof the resin, and is equivalent to the drawability of the resin. LLDPE,having more linear molecular chains, might be thought to have a highervelocity at break. This, however, may be offset by the increased forcerequired to break the chain entanglement in the LDPE, compared to therelatively non-entangled LLDPE. Thus, depending on the characteristicsof the specific blend used, either the LDPE (as in blends A and B) orthe LLDPE (as in blend C) may have a higher velocity at break.

[0057] Whichever is higher, one would expect the transition between thetwo to be relatively linear for different percentages of the twoplastics. Surprisingly, however, adding LLDPE to LDPE seems to producean increase in velocity at break that goes beyond the higher velocity atbreak of the other component, implying a synergistic effect. This isparticularly noticeable between around 30% of LLDPE and around 70% ofLLDPE, in resin form.

[0058]FIG. 3 shows how the force of the different blends, and thedifferent proportions of the different blends, varies at differentvelocities or pull-off speeds. As shown, the blended versions allrequire a greater force to achieve any given velocity or pull-off speedthan either 100% LDPE or 100% LLDPE. Again, therefore, surprisingly, acombination of LDPE and LLDPE has better properties than either of thetwo plastics alone. A blend of 80% LDPE and 20% LLDPE seems to haveparticularly good qualities in these resins.

[0059]FIG. 4 also shows the synergistic effect for force to break andvelocity to break (or drawability) of the resin.

[0060] Following these experiments with resin, a further set ofexperiments were conducted by the applicant with foam. These experimentswere conducted using LDPE having a melt flow rate (“MFR”) of 2 g/10minutes and a density of 923 kg/m³, and conventional Ziegler-Natta LLDPEhaving an MFR of 2.7 g/10 minutes and a density of 918 kg/m³.

[0061] To manufacture the foam, the LLDPE was mixed with the LDPE andextruded using a single-screw or a twin-screw extruder. The blowingagent used was butane.

[0062] The experiments are described in more detail below, but some ofthe results showed that under the same processing conditions (that is:blowing agent weight, total feed rate, and line speed), there was nosubstantial foam density increase when certain quantities of LLDPE wereadded to the LDPE.

[0063] In fact, surprisingly, at a higher percentage addition of LLDPE,the foam density was reduced to slightly below the same level as for100% LDPE. In these experiments, the optimum seems to be from about 20%to about 25% LLDPE addition. Since LLDPE is currently only 92.5% of thecost of LDPE, this means a cost saving of 1.5% to 1.9%, and a furtherbenefit is the improved toughness and elasticity of foams having LLDPEadded.

[0064] Another interesting point may be noted. Materials having a lowermelt flow index (“MFI”) are generally more difficult to foam to a goodquality, since greater sheer force tends to be generated during theextrusion process. Using this method, however, it was possible toproduce a good quality foam using a LLDPE resin having a low melt flowindex, less than 10 g/10 minutes, preferably less than 5 g/10 minutes,and more preferably less than 3 g/10 minutes. One specific example of anLLDPE resin is 2.8 g/10 minutes.

[0065] No foam collapse was observed at higher LLDPE levels (up to 25%)in these runs, and the foam that was produced seemed to be of a similarlevel of effectiveness to that made using 100% LDPE.

[0066] Four different examples of the experiments made will now bedescribed, purely to illustrate the invention. One of these used asingle-screw extruder and three of these used a twin-screw extruder.

Example 1

[0067] TABLE 1 Foam Thick- Run LDPE density ness Foam Melt No. wt %LLDPE kg/m³ mm quality temp. ° C. 1 100 0 21.1 1.0 good 96-97 2 75 2521.4 1.1 good 97 3 65 35 21.2 1.1 good 97

[0068] For the first set of these experiments a 120 mm single-screwextruder was used to manufacture a foam sheet. The first one run wasused as a control run, using 100% LDPE.

[0069] In the second and third runs of Table 1, with 25% and 35% LLDPErespectively, the foam quality and density obtained were comparable tothat of the foam obtained using 100% LDPE, although it was necessary toadjust the process conditions to control the melt temperature.

Example 2

[0070] TABLE 2 Foam thick- Run LDPE LLDPE density ness Foam Melt. No. wt% wt % kg/m³ mm quality Temp. ° C. 1 100 0 24.2 0.8 good 111 2 90.5 9.524.9 0.8 good 112 3 87.1 12.9 24.5 0.8 good 112 4 83.8 16.2 24.3 0.8good 112 5 80.5 19.5 24.1 0.8 good 112 6 74.8 25.2 24.1 0.8 good 112

[0071] Table 2 shows the results obtained from an experiment withtwin-screw extruders. The twin-screw extruder was 150 mm in diameter andwas used for producing a 0.8 mm sheet of foam from a blend of LDPE andLLDPE. The blowing agent used was an iso-/n-butane mixture.

[0072] Again, the first run was used as a control run using 100% LDPE.In runs 2 through 6, the amount of LDPE was steadily reduced and theamount of LLDPE was steadily increased. Table 2 shows that foam densityactually decreased for 19.5% and 25.2% LLDPE, runs 5 and 6 respectively.The foam quality was good for all blends and it was not necessary toadjust the process conditions to control the melt temperature.

Example 3

[0073] TABLE 3 Foam thick- Run LDPE LLDPE density ness Foam Melt. No. Wt% Wt % kg/m³ mm quality Temp. ° C. 1 100 0 22.7 0.8 good 108 2 95 5 22.90.8 good 109 3 85 15 22.7 0.8 slight 111-112 collapse 4 80 20 22.9 0.8slight 111-112 collapse 5 75 25 22.9 0.8 slight 111-112 collapse 6 70 3022.7 0.8 good 109-110

[0074] In this experiment, a 150 mm twin-screw extruder was used forproducing a 0.8 mm sheet of foam from an LDPE and LLDPE blend. Run 1 ofTable 1 was used as a control run with 100% LDPE. Runs 2 to 6 show theeffects of steadily increasing the percentage of LLDPE. When the LLDPEwas increased to 15% (run 3) through to 25% (run 5) the melt temperaturebecame higher and foam quality degraded. Before run 6, changes inprocess conditions were made that brought the melt temperature down andconsequently the foam quality was again fully comparable to the controlvalue. As with Example 1, it was necessary to adjust the processconditions to control the melt temperature.

[0075] With the addition of 30% LLDPE, it can be noted that a foamquality and density was achieved that is fully comparable to the 100%LDPE formulation.

Example 4

[0076] TABLE 4 Foam thick- Run LDPE LLDPE density ness Foam Melt. No. Wt% Wt % kg/m³ mm quality Temp. ° C. 1 100 0 17.4 3.0 good 107 2 90 1017.6 3.0 good 107-108 3 85 15 17.4 3.0 good 108 4 80 20 17.4 3.1 good109 5 75 25 17.4 3.1 good 109 6 65 35 17.2 3.1 good 109 7 55 45 17.4 3.0fair 110-111 8 45 55 17.0 3.2 good 108-109

[0077] The data shown in Table 4 are the results from a furtherexperiment using a twin-screw extruder having a 150 mm diameter. In thisexample, an extruder was used to produce a 3 mm sheet of foam from ablend of LDPE and LLDPE. As can be seen from the table, the melttemperatures for the LDPE/LLDPE blends in runs 2-6 were only slightlyhigher than the melt temperature for the controlled run (run 1). Thus,there was no need to change the process conditions and the foam qualityremained good, in that no collapse or significant density increase wasobserved. In run 7, the temperature was raised by 4° C. and the foamquality degraded. The process conditions, specifically the temperatureon the output of the extruder, were altered and, in run 8 the melttemperature remained fairly low and the foam quality was again fullycomparable to that of the controlled run, the foam density actuallybeing lower.

[0078] In all of these runs, by adding LLDPE to LDPE, and whereappropriate, by controlling the melt temperature, a foam quality anddensity was achieved which is fully comparable or even better, than thatachievable using 100% LDPE.

[0079] When it is appropriate to control the process conditions, thereare many parameters that can be altered. In these runs, the outputtemperature of the extruder was set by adjusting the amount of waterflowing to the heat exchanger on the output. Another way of doing thisis to adjust the temperature set point of the electrical heating elementon the output. It is also possible to control the shear heat generatedby the mechanical action of the extruder by, for example, adjusting thethroughput, and other methods of controlling the melt temperature willreadily occur to the skilled person.

[0080] Surprisingly, no significant increase in weight was found inthese experiments for foams derived from a blend of LDPE and LLDPE, evenat low levels of LLDPE. In fact, it was found to be possible to extrudefoams containing up to 35% LLDPE on the single-screw extruder, and foamscontaining up to 55% LLDPE on the twin-screw extruder. Such foams wouldrepresent a significant cost saving compared to 100% LDPE foams, orfoams produced using metallocene-catalyzed LLDPE, or havingcross-linking agents added.

[0081] As an alternative to using LDPE, it is possible to use otherpolyolefins, such as polypropylene, particularly a high-melt strengthpolypropylene. Non cross-linked resins, or resins with a relativelysmall amount of cross-linking, are particularly suitable.

[0082] In the present specification, “comprises” means “includes orconsists of” and “comprising” means “including or consisting of”

[0083] The features disclosed in the foregoing description, or thefollowing claims, or the accompanying drawings, expressed in theirspecific forms or in terms of a means for performing the disclosedfunction, or a method or process for attaining the disclosed result, asappropriate, may, separately, or in any combination of such features, beutilised for realising the invention in diverse forms thereof.

[0084] While particular embodiments and applications of the presentinvention have been illustrated and described, it is to be understoodthat the invention is not limited to the precise construction andcompositions disclosed herein and that various modifications, changes,and variations may be apparent from the foregoing descriptions withoutdeparting from the spirit and scope of the invention as defined in theappended claims.

What is claimed is:
 1. A non-crosslinked polyolefin foam comprising aplastics component and a blowing agent, the plastics componentcomprising a first constituent and a second constituent, wherein thefirst constituent is a Ziegler-Natta catalyzed linear low densitypolyolefin and the second constituent is a low density polyolefin, andwherein the Ziegler-Natta catalyzed linear low density polyolefin has apolydispersity of less than 10 and a melt flow index less than 10 g/10minutes.
 2. The polyolefin foam of claim 1, wherein the secondconstituent is a low density polyethylene.
 3. The polyolefin foam ofclaim 1, wherein the plastics component comprises from 1% to 85% byweight of the first constituent, and from 99% to 15% by weight of thesecond constituent.
 4. The polyolefin foam of claim 3, wherein theplastics component comprises from 5% to 10% by weight of the firstconstituent, and from 95% to 90% by weight of the second constituent. 5.The polyolefin foam of claim 4, wherein the plastics component comprisesfrom 10% to 15% by weight of the first constituent, and from 90% to 85%by weight of the second constituent.
 6. The polyolefin foam of claim 5,wherein the plastics component comprises primarily of from 15% to 20% byweight of the first constituent, and from 85% to 80% by weight of thesecond constituent.
 7. The polyolefin foam of claim 6, wherein theplastics component comprises primarily of from 20% to 25% by weight ofthe first constituent, and from 80% to 75% by weight of the secondconstituent.
 8. The polyolefin foam of claim 7, wherein the plasticscomponent comprises primarily of from 25% to 30% by weight of the firstconstituent, and from 75% to 70% by weight of the second constituent. 9.The polyolefin foam of claim 8, wherein the plastics component comprisesprimarily of from 30% to 35% by weight of the first constituent, andfrom 70% to 65% by weight of the second constituent. 10 The polyolefinfoam of claim 9, wherein the plastics component comprises primarily offrom 35% to 40% by weight of the first constituent, and from 65% to 60%by weight of the second constituent.
 11. The polyolefin foam of claim 1,wherein the form has a density less than 90 kg/m³.
 12. The polyolefinfoam of claim 11, wherein the form has a density less than 30 kg/m³. 13.The polyolefin foam of claim 1, wherein the polyolefin foam is aclosed-cell foam.
 14. The polyolefin foam of claim 1, wherein thedensity of the first constituent is from 917 to 930 kg/m³.
 15. Thepolyolefin foam of claim 1, wherein the crystallization temperatures ofthe two constituents differ by more than 8° C.
 16. The polyolefin foamof claim 15, wherein the crystallization temperatures differ by morethan 12° C.
 17. The polyolefin foam of claim 1, wherein the melt flowindex of the Ziegler-Natta catalyzed linear low density polyolefin isless than 5 g/10 minutes.
 18. The polyolefin foam of claim 1, whereinthe melt flow index of the Ziegler-Natta catalyzed linear low densitypolyolefin is less than 3 g/10 minutes.
 19. The polyolefin foam of claim1, wherein the polydispersity of the Ziegler-Natta catalyzed linear lowdensity polyolefin is less than
 8. 20. The polyolefin foam of claim 19,wherein the polydispersity of the Ziegler-Natta catalyzed linear lowdensity polyolefin is less than
 5. 21. The polyolefin foam of claim 1further including nucleating agents and aging agents.
 22. Anon-crosslinked polyolefin foam comprising a plastics component and ablowing agent, the plastics component comprising a first constituent anda second constituent, wherein the first constituent is a Ziegler-Nattacatalyzed linear low density polyethylene and the second constituent isa polypropylene, and wherein the Ziegler-Natta catalyzed linear lowdensity polyolefin has a polydispersity of less than 10 and a melt flowindex less than 10 g/10 minutes.
 23. The polyolefin foam of claim 22,wherein the second constituent is a high-melt strength polypropylene.24. The polyolefin foam of claim 22, wherein the plastics componentcomprises from 1% to 85% by weight of the first constituent, and from99% to 15% by weight of the second constituent.
 25. The polyolefin foamof claim 24, wherein the plastics component comprises from 5% to 10% byweight of the first constituent, and from 95% to 90% by weight of thesecond constituent.
 26. The polyolefin foam of claim 25, wherein theplastics component comprises from 10% to 15% by weight of the firstconstituent, and from 90% to 85% by weight of the second constituent.27. The polyolefin foam of claim 26, wherein the plastics componentcomprises primarily of from 15% to 20% by weight of the firstconstituent, and from 85% to 80% by weight of the second constituent.28. The polyolefin foam of claim 27, wherein the plastics componentcomprises primarily of from 20% to 25% by weight of the firstconstituent, and from 80% to 75% by weight of the second constituent.29. The polyolefin foam of claim 28, wherein the plastics componentcomprises primarily of from 25% to 30% by weight of the firstconstituent, and from 75% to 70% by weight of the second constituent.30. The polyolefin foam of claim 29, wherein the plastics componentcomprises primarily of from 30% to 35% by weight of the firstconstituent, and from 70% to 65% by weight of the second constituent.31. The polyolefin foam of claim 30, wherein the plastics componentcomprises primarily of from 35% to 40% by weight of the firstconstituent, and from 65% to 60% by weight of the second constituent.32. The polyolefin foam of claim 22, wherein the form has a density lessthan 90 kg/m³.
 33. The polyolefin foam of claim 32, wherein the form hasa density less than 30 kg/m³.
 34. The polyolefin foam of claim 22,wherein the polyolefin foam is a closed-cell foam.
 35. The polyolefinfoam of claim 22, wherein the density of the first constituent is from917 to 930 kg/m³.
 36. The polyolefin foam of claim 22, wherein thecrystallization temperatures of the two constituents differ by more than8° C.
 37. The polyolefin foam of claim 36, wherein the crystallizationtemperatures differ by more than 12° C.
 38. The polyolefin foam of claim22, wherein the melt flow index of the Ziegler-Natta catalyzed linearlow density polyolefin is less than 5 g/10 minutes.
 39. The polyolefinfoam of claim 38, wherein the melt flow index of the Ziegler-Nattacatalyzed linear low density polyolefin is less than 3 g/10 minutes. 40.The polyolefin foam of claim 22, wherein the polydispersity of theZiegler-Natta catalyzed linear low density polyolefin is less than 8.41. The polyolefin foam of claim 40, wherein the polydispersity of theZiegler-Natta catalyzed linear low density polyolefin is less than 5.42. The polyolefin foam of claim 22 further including nucleating agentsand aging agents.
 43. A method of manufacturing a non-crosslinkedpolyolefin foam comprising mixing a resin comprising a first constituentand a second constituent in an extruder, adding a blowing agent to theresulting mixture, and extruding the resulting mix into foam form,wherein the first constituent is a Ziegler-Natta catalyzed linear lowdensity polyolefin and the second constituent is a low densitypolyolefin, and wherein the Ziegler-Natta catalyzed linear low densitypolyolefin has a polydispersity of less than 10 and a melt flow indexless than 10 g/10 minutes.
 44. The method of claim 43, wherein thesecond constituent is a low density polyethylene.
 45. The method ofclaim 43, wherein the first constituent is present in an amount from 1%to 85% by weight of the total polyolefin content.
 46. The method ofclaim 45, wherein the first constituent is present in an amount from 5%to 10% by weight of the total polyolefin content.
 47. The method ofclaim 46, wherein the first constituent is present in an amount from 10%to 15% by weight of the total polyolefin content.
 48. The method ofclaim 47, wherein the first constituent is present in an amount from 15%to 20% by weight of the total polyolefin content.
 49. The method ofclaim 48, wherein the first constituent is present in an amount from 20%to 25% by weight of the total polyolefin content.
 50. The method ofclaim 49, wherein the first constituent is present in an amount from 25%to 30% by weight of the total polyolefin content.
 51. The method ofclaim 50, wherein the first constituent is present in an amount from 30%to 35% by weight of the total polyolefin content.
 52. The method ofclaim 51, wherein the first constituent is present in an amount from 35%to 40% by weight of the total polyolefin content.
 53. The method ofclaim 43, wherein the foam is extruded to a density of less than 90kg/m³.
 54. The method of claim 43, wherein the foam is a closed-cellfoam.
 55. The method of claim 43, wherein the density is from 917 to 930kg/m³.
 56. The method of claim 43, wherein the crystallizationtemperatures of the first and second constituents differ by more than 8°C.
 57. The method of claim 56, wherein the crystallization temperaturesof the first and second constituents differ by more than 12° C.
 58. Themethod of claim 43, wherein the first constituent has a melt flow indexof less than 5 g/10 minutes.
 59. The method of claim 58, wherein thefirst constituent has a melt flow index of less than 3 g/10 minutes. 60.The method of claim 43, wherein the polydispersity of the Ziegler-Nattacatalyzed linear low density polyolefin is less than
 8. 61. The methodof claim 60, wherein the polydispersity of the Ziegler-Natta catalyzedlinear low density polyolefin is less than
 5. 62. The method of claim43, further including mixing nucleating agents and aging agents with thefirst and second constituents.
 63. The method of claim 43, wherein theresultant mixture is extruded in a twin-screw extruder.
 64. The methodof claim 43 further including controlling the melt temperature of themix during extruding.
 65. The method of claim 64, wherein controllingthe melt temperature includes matching the melt temperature of the mixto a pre-determined datum.
 66. The method of claim 65, wherein thepre-determined datum is determined by extruding 100% of the secondconstituent.
 67. The foam produced according to the method of claim 43.68. A method of manufacturing a non-crosslinked polyolefin foamcomprising mixing a resin comprising a first constituent and a secondconstituent in an extruder, adding a blowing agent to the resultingmixture, and extruding the resultant mix into foam form, wherein thefirst constituent is a Ziegler-Natta catalyzed linear low densitypolyethylene and the second constituent is a polypropylene, and whereinthe Ziegler-Natta catalyzed linear low density polyolefin has apolydispersity of less than 10 and a melt flow index less than 10 g/10minutes.
 69. The method of claim 68, wherein the second constituent is ahigh-melt strength polypropylene.
 70. The method of claim 68, whereinthe first constituent is present in an amount from 1% to 85% by weightof the total polyolefin content.
 71. The method of claim 70, wherein thefirst constituent is present in an amount from 5% to 10% by weight ofthe total polyolefin content.
 72. The method of claim 71, wherein thefirst constituent is present in an amount from 10% to 15% by weight ofthe total polyolefin content.
 73. The method of claim 72, wherein thefirst constituent is present in an amount from 15% to 20% by weight ofthe total polyolefin content.
 74. The method of claim 73, wherein thefirst constituent is present in an amount from 20% to 25% by weight ofthe total polyolefin content.
 75. The method of claim 74, wherein thefirst constituent is present in an amount from 25% to 30% by weight ofthe total polyolefin content.
 76. The method of claim 75, wherein thefirst constituent is present in an amount from 30% to 35% by weight ofthe total polyolefin content.
 77. The method of claim 76, wherein thefirst constituent is present in an amount from 35% to 40% by weight ofthe total polyolefin content.
 78. The method of claim 68, wherein thefoam is extruded to a density of less than 90 kg/m³.
 79. The method ofclaim 68, wherein the foam is a closed-cell foam.
 80. The method ofclaim 68, wherein the density is from 917 to 930 kg/m³.
 81. The methodof claim 68, wherein the crystallization temperatures of the first andsecond constituents differ by more than 8° C.
 82. The method of claim81, wherein the crystallization temperatures of the first and secondconstituents differ by more than 12° C.
 83. The method of claim 68,wherein the first constituent has a melt flow index of less than 5 g/10minutes.
 84. The method of claim 83, wherein the first constituent has amelt flow index of less than 3 g/10 minutes.
 85. The method of claim 68,wherein the polydispersity of the Ziegler-Natta catalyzed linear lowdensity polyolefin is less than
 8. 86. The method of claim 85, whereinthe polydispersity of the Ziegler-Natta catalyzed linear low densitypolyolefin is less than
 5. 87. The method of claim 68, further includingmixing nucleating agents and aging agents with the first and secondconstituents.
 88. The method of claim 68, wherein the resultant mixtureis extruded in a twin-screw extruder.
 89. The method of claim 68 furtherincluding controlling the melt temperature of the mix during extruding.90. The method of claim 89, wherein controlling the melt temperatureincludes matching the melt temperature of the mix to a pre-determineddatum.
 91. The method of claim 90, wherein the pre-determined datum isdetermined by extruding 100% of the second constituent.
 92. The foamproduced according to the method of claim 68.